Urethane coating composition and process

Abstract

Urethane coatings having improved weather and erosion resistant properties are provided by applying and curing in an atmosphere containing moisture a coating composition comprising (1) an isocyanate-terminated prepolymer comprised of the reaction product of (a) a polytetramethylene ether glycol having an average molecular weight between about 500 and about 700, (b) an oxyalkylated triol having an average molecular weight between about 400 and about 1000 in an amount between 0 and about 20 percent by weight based on the combined weight of the oxyalkylated triol and the polytetramethylene ether glycol, and (c) an organic diisocyanate and (2) an inert organic solvent. These coatings are particularly suitable for helicopter blades, radomes, leading edges of aircraft, and the like.

What is claimed is: 
     
       1. A flexible urethane coating composition comprising a solvent and an isocyanate-terminated prepolymer comprising the reaction product of (a) a polytetramethylene ether glycol having an average molecular weight between about 500 and about 700,   (b) an oxyalkylated triol having an average molecular weight between about 400 and about 1000, in an amount between about 8 and about 12 percent by weight based on the combined weight of said oxyalkylated triol and said polytetramethylene ether glycol, and   (c) an organic diisocyanate in a proportion sufficient to provide between about 1.2 and about 1.8 -NCO groups for each -OH group in said polytetramethylene ether glycol and said oxyalkylated triol.   
     
     
       2. The coating composition of claim 1 wherein said oxyalkylated triol is the product of oxyalkylating a triol with an alkylene oxide selected from the group consisting of ethylene oxide, propylene oxide, butylene oxide, and mixtures thereof. 
     
     
       3. The coating composition of claim 2 wherein said organic diisocyanate is toluene diisocyanate. 
     
     
       4. The coating composition of claim 3 wherein said triol is an aliphatic triol. 
     
     
       5. The coating composition of claim 4 wherein the proportion of said organic diisocyanate is sufficient to provide from about 1.4 to about 1.6--NCO groups per each --OH group in said polytetramethylene ether glycol and said oxyalkylated triol. 
     
     
       6. The coating composition of claim 5 wherein said triol is glycerin. 
     
     
       7. The flexible coating forming composition of claim 6 wherein said oxyalkylated triol is oxypropylated glycerin having an average molecular weight of about 600.